The Lower East Side fireplug gushes out a flood of money for the city — some $33,000 a year, according to one estimate — by luring unwary drivers who think they’re parking in a legal spot.

The drivers blame two factors: white lines on the street that are easily mistaken for wide “boxes’’ where parking is permitted; and a sidewalk extension masquerading as a bike lane.

The hydrant — on Forsyth Street, opposite 152 Forsyth St. — has netted 187 summonses from unsuspecting drivers between Aug. 1, 2013, and March 26 of this year, according to Ben Wellington, a statistics professor at Pratt Institute. At $115 each, that works out to $21,505.

Wellington estimates the hydrant — which generates the most money of any of the city’s approximately 110,000 such fire-protection devices — helps keep the city liquid to the tune of $33,118 annually.

“It’s unbelievable how often the cops come by here,” said Sharon Hoahing, who works nearby. “I have no problem with them saying, ‘You can’t park there’ if it’s a hydrant, but mark it off correctly.”

The white lines painted on the street are incredibly misleading, neighbors said. Two sets of lines decorate the street between the curb extension and the traffic lanes, but there’s a big problem: The space between the lines, easily wide enough for a car, is marked with diagonal lines at some points — but not in front of the hydrant. Drivers think it’s legal to park where the lines end.

The fire hydrant has a sign in Chinese warning of fines associated with parking in front of it.Photo: Brigitte Stelzer

The curb extension was installed in 2008 to provide more room for pedestrians walking along the east side of Sara D. Roosevelt Park, according to a spokesman for the city Department of Transportation. The trouble is that it’s separated from the original curb by a raised strip of cobblestones with trees planted in them — and that, many people think, is where the sidewalk ends.

Adding to the confusion, there’s a widespread misconception it’s always legal to park on the traffic-side line when a bike lane is between the sidewalk and the traffic lanes — even when a hydrant is on the sidewalk. But it’s OK only if there’s a sign specifically permitting parking there.

“I had no idea it was a hydrant, it was set so far back,” said Steven Harvey, 60, who got a ticket.

Harvey was stunned to learn the gap was not a bike lane — even though bikers often use it as such.

“What are they talking about, that’s not a bike lane?” Harvey asked. “That doesn’t make sense to me.”